The present invention relates generally to a battery charging system, a charge control apparatus, and a charge control method for use in a computer, and particularly to a charging system for charging a rechargeable battery included in an intelligent battery, a charge control apparatus for controlling charge for a battery included in a power supply unit, a charge control method, and a computer employing the charge control method.
As mobile computing has become pervasive, portable personal computers (hereinafter referred to as portable PCs) having various sizes and functions have been developed. For instance, they include notebook PC, sub-notebook PC, palmtop PC, and PDA (Personal Digital Assistant).
A portable PC includes an internal battery which is generally removable. This allows a user to operate the portable PC in an environment in which no commercial power supply is available, for instance, in a train. A secondary battery is usually employed s the internal battery which can be repeatedly used by charging.
Conventionally, to charge such a secondary battery, the charging voltage is set to the maximum allowable voltage of the battery to maximize the capacity at the beginning of using the battery (hereinafter referred to as xe2x80x9cinitial capacityxe2x80x9d).
However, in the above described conventional technique in which the charging is carried out with the charging voltage set to the maximum voltage of the battery, there is a problem that the life of the battery is shorter than the case in which the charging is performed using a charging voltage lower than the allowable maximum voltage.
Also, the secondary battery is generally characterized in that the total capacity decreases as the discharging and charging are repeated. Further, the decrease in the total capacity is more noticeable as the charging voltage is higher.
FIG. 16 shows an example of the charging characteristics of a lithium-ion battery single cell having a voltage rating of 4.2 V, for charging voltages of 4.10 V and 4.20 V. The ordinate in this figure represents the percentage ratio of capacity to the initial capacity (hereinafter referred to axe2x80x9ccapacity ratioxe2x80x9d). Accordingly, although the capacity ratio associated with zero charging/discharging cycles is 100% for both charging voltages of 4.10 V and 4.20 V, the actual capacity is different for each charging voltage. Further, the above-described number of charging/discharging cycles means the number of times the discharging is performed until the battery capacity becomes 0% after the charging is performed from 0% to 100% of the battery capacity. As shown in the FIG. 16, the capacity ratio decreases as the number of charging/discharging cycles increases, and the decrease in the capacity ratio is greater for the higher charging voltage.
Accordingly, in the prior art in which charging is performed with the charging voltage set to the allowable maximum voltage of the battery, the battery life is shorter as compared with the case in which charging is performed with a charging voltage lower than the allowable maximum voltage.
The present invention seeks to solve the above problems, and has as its object the provision of a charging system which enables an increase in the initial capacity of a rechargeable battery whilst also prolonging the battery life.
In accordance with a charging system according to the present invention, a rechargeable battery included in an intelligent battery is charged by a charging device for which a charging condition can be set. The above battery may be any suitable battery type including: lithium-ion battery, nickel-hydrogen battery, nickel-cadmium battery, lithium-polymer battery, or equivalent.
The charging system of the present invention further includes a controller for receiving deterioration information related to the deterioration of the battery. The controller uses this deterioration information to set a charging condition of the charging device to increase battery capacity until the deterioration information meets a predetermined condition, and to set a different charging condition to increase battery life after the deterioration information meets the predetermined condition.
For instance, as a charging condition for increasing the battery capacity when a lithium-ion battery is used, the charging voltage is set to the allowable maximum voltage of the battery or to a predetermined voltage smaller but in the vicinity of the allowable maximum voltage, and similarly, as the charging condition for making the battery life longer, the charging voltage is set to a voltage lower than the charging voltage which is applied as the charging condition for increasing battery capacity.
The above-mentioned predetermined condition is used to indicate the timing for switching a charging condition from giving priority to a higher capacity to giving priority to a longer life. If, for instance, the user of the intelligent battery prefers a longer life to a higher capacity for the battery, a mode can be applied for setting the above predetermined condition to be met when the deterioration information indicates a lower degree of deterioration, and conversely, if the user prefers a higher capacity to a longer life for the battery, a mode can be applied for setting the above predetermined condition to be met when the deterioration information indicates a higher degree of deterioration. In this case, either the individual users may set the predetermined condition, or the predetermined condition may be set based on previous statistical examination of the intentions of users.
Further, regardless of the user""s intention, for instance, the condition indicating the timing that can maximize the accumulated value of total capacities to the life of the battery provided in the intelligent battery related to the present invention (generally the period until the total capacity of a full-charged battery becomes 60% of the initial capacity) can be previously obtained by an experiment, computer simulation, or the like, and this condition can be applied as the above predetermined condition.
As described above, since the charging system of the present invention receives the deterioration information related to the deterioration of a battery from the intelligent battery, sets the charging condition of the charging device to make the battery capacity higher until the deterioration information meets a predetermined condition, and sets the charging condition to make the battery life longer after the deterioration information meets the predetermined condition, the initial capacity of the battery can be made larger and the life of the battery can be made longer.
The deterioration information of the charging system may be at least one of: the number of charging/discharging cycles of the battery, the capacity of the battery, and a value corresponding to the internal resistance of the battery.
That is, as described with reference to FIG. 16, since a rechargeable battery is generally characterized in that its total capacity decreases as the number of charging/discharging cycles increases, the number of charging/discharging cycles of the battery can be applied as information indicating the deterioration state of the battery. Further, any information that can provide the capacity of the battery can also be applied as information indicating the deterioration state of the battery. Furthermore, since a deteriorated battery usually tends to have an increase in internal impedance, the degree of deterioration of the battery can be determined based on a value corresponding to the internal resistance of the battery. Therefore, the value corresponding to the internal resistance of the battery can be applied as information indicating the deterioration state of the battery.
Further, if the number of charging/discharging cycles of the battery is included in the deterioration information, it can be assumed that the number of charging/discharging cycles is detected in a manner in which the charging amount or discharging amount of the battery is detected, and for the detected amount, the total capacity of the battery or a capacity obtained by multiplying the total capacity of the battery by a predetermined coefficient is employed as unit cycle. The reason for this is described below.
FIG. 15 shows an example of the actual measurement result of the cycle characteristics for a partial discharge and a 100% discharge of an existing battery. The measurement conditions for this are shown below.
Battery: Lithium-ion battery single cell
Temperature: 25xc2x0 C.
Charging method: Constant voltage, constant current charging method (constant voltage: 4.2 V, constant current: 1.6 A)
Charging time: A three-hour charging was performed unconditionally.
Method for capacity measurement: When each partial discharge reached 100 cycles, discharging was performed with a 1.6 A constant current discharge until the battery voltage reached 2.75 V, and the capacity was measured.
The abscissa in FIG. 15 represents the number of charging/discharging cycles on a 100% discharge basis. That is, for a 20% partial discharge, the number of charging/discharging cycles is counted as one when the 20% partial discharge is repeated five times.
As shown in the same figure, the 20% partial discharge, 30% partial discharge, and 50% partial discharge are on substantially the same line. However, for the 20% partial discharge, it slightly deviates from the line when the number of charging/discharging cycles becomes 350 or larger. The reason for this is considered to be the occurrence of deterioration due to the three-hour constant-time charging. That is, the capacity reaches 100% in a short time by the charging, but the continuation of the charging causes the deterioration. In electronic equipment, however, since the charging is usually stopped when the capacity reaches 100%, it seems that the 20% partial discharge also lies on the same line as the 30% partial discharge and 50% partial discharge.
From the foregoing, it is possible that the charging amount or the discharging amount is accumulated, and one cycle is counted when the accumulated amount equals an amount obtained by multiplying the total capacity of the battery by a predetermined coefficient (about 0.9 for the battery of FIG. 15), and the battery capacity can be estimated from the number of charging/discharging cycles.
Since the number of charging/discharging cycles of the battery can be detected employing the total battery capacity or alternatively by a capacity obtained by multiplying the total battery capacity by a predetermined coefficient as unit cycle, as described above, the number of charging/discharging cycles can be simply and accurately detected even if the battery capacity does not reach zero or a predetermined capacity in the vicinity of zero.
The charging condition employed in the present invention may be the charging voltage of the battery or the determination condition for charging termination of the battery.
That is, for instance, since the charging of a lithium-ion battery is carried out by the constant-current, constant-voltage method, the charging voltage can be switched to change the charging condition from that for making the battery capacity higher to that for making the battery life longer. Further, for instance, the charging of the nickel-hydrogen battery employs the constant-current charging method, and the completion of the charging is determined by the value of xcex94T which is a temperature elevation value based on the temperature at the beginning of the charging, or the value of xcex94T/xcex94t which is a temperature elevation value per unit time. Accordingly, for the nickel-hydrogen battery, by changing the determination condition for charging termination of at least either of xcex94T or xcex94T/xcex94t, the charging condition can be changed from that for making the battery capacity higher to that for making the battery life longer. Further, for instance, the nickel-cadmium battery terminates the charging by detecting a change in the battery voltage. Accordingly, for the nickel-cadmium battery, by changing the determination condition for charging termination based on the deviation of the battery voltage, the charging condition can be switched from that for making the battery capacity higher to that for making the battery life longer.
According to other aspects of the invention, a charge control apparatus and charge control method are used to control the charging of a rechargeable battery included in a power supply unit. Deterioration information indicating the deterioration state of the battery is detected, and the charging condition for the battery is set to make the battery capacity higher until the deterioration information meets a predetermined condition, and the charging condition is set to make the battery life longer after the deterioration information meets the predetermined condition. The above battery may be one of lithium-ion battery, nickel-hydrogen battery, nickel-cadmium battery, lithium-polymer battery, and the like.
Accordingly, since the charge control apparatus and charge control method related to the present invention operate in a manner similar to the charging system related to the present invention, the initial capacity of the battery included in the power supply unit can be increased and the battery life can be also be increased. The deterioration information may be one of: the number of charging/discharging cycles of the battery, the capacity of the battery, and a value corresponding to the internal resistance of the battery.
Also, in the charge control apparatus and charge control method related to the present invention, where the number of charging/discharging cycles of the battery is employed as the deterioration information, the discharging amount or charging amount of the battery is detected, and for the detected amount, the number of the charging/discharging cycles of the battery can be detected by employing the total capacity of the battery or a capacity obtained by multiplying the total capacity of the battery by a predetermined coefficient as unit cycle. By this, the number of charging/discharging cycles can be simply and accurately counted even if the battery capacity is not zero or a predetermined capacity in the vicinity of zero.
Further, in the charging control apparatus and charging control method of the present invention, the charging condition can be the charging voltage of the battery or the determination condition for charging termination of the battery.
Further, to apply the charging control method related to the present invention to a computer including a CPU, a memory, a display, and input devices, which are interconnected by a bus, it can be implemented by making the memory from a machine-readable recording medium having recorded thereon a program for controlling the charging to the battery according to the charging control method of the present invention.
Further, to apply the charging control method related to the present invention to a computer including a CPU, a memory, a display, input devices, and a network connection device, which are interconnected by a bus, it can be implemented by employing, as the external storage device of the server computers arranged on a network connected by the network connection device, a machine-readable recording medium having recorded thereon a program for controlling the charging to the battery according to the charging control method of the present invention.